Flutter默认生成的项目是没有设置启动图的，并且打开APP显示主页之前会有短暂的黑屏，

1. 手动设置启动页，android/app/src/main/res/drawable/launch_background.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Modify this file to customize your launch splash screen -->
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- <item android:drawable="@android:color/white" /> -->

    <!-- You can insert your own image assets here -->
    <item>
        <bitmap android:src="@mipmap/splash" android:mipMap="true" android:filter="true"  />
    </item>
</layer-list>

2. 在mipmap中需要放入图片资源文件
3. 在AndroidManifest.xml加入以下两行代码

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.newretail.seller">
    <!-- io.flutter.app.FlutterApplication is an android.app.Application that
         calls FlutterMain.startInitialization(this); in its onCreate method.
         In most cases you can leave this as-is, but you if you want to provide
         additional functionality it is fine to subclass or reimplement
         FlutterApplication and put your custom class here. -->
    <application
        android:name="io.flutter.app.FlutterApplication"
        android:label="Flutter"
        android:icon="@mipmap/ic_launcher">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop"
            android:theme="@style/LaunchTheme"
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
            android:hardwareAccelerated="true"
            android:value = "true"
            android:windowSoftInputMode="adjustResize">
            
            <!--加入开始-->
            <meta-data
                android:name="io.flutter.app.android.SplashScreenUntilFirstFrame"
                android:value="true" />
            <meta-data
                android:name="io.flutter.embedding.android.SplashScreenDrawable"
                android:resource="@drawable/launch_background" />
            <!--加入结束-->
            
            <intent-filter>
                <action android:name="android.intent.action.MAIN"/>
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>
        </activity>
        <!-- Don't delete the meta-data below.
             This is used by the Flutter tool to generate GeneratedPluginRegistrant.java -->
        <meta-data
            android:name="flutterEmbedding"
            android:value="2" />
    </application>
</manifest>

4. 保存，运行 “flutter run”。